1. Field of the Invention
The present invention relates to a surface light source using white light emitting diodes (LEDs) and a liquid crystal display (LCD) backlight unit having the same, and more particularly, to a surface light source capable of producing uniform white light overall using white light emitting diodes, and an LCD backlight unit having the same.
2. Description of the Related Art
A cold cathode fluorescent lamp (CCFL) used as a light source of a conventional liquid crystal display (LCD) employs mercury gas, which may trigger environmental pollution. Besides, the CCFL is slow in response rate, low in color reproducibility and inappropriate for a smaller-sized and lighter-weight LCD panel.
In contrast, a light emitting diode (LED) is environment-friendly, high in response rate with several nano seconds, thus effective for a video signal stream and impulsively driven. Moreover, the LED is capable of reproducing color by 100% and varying brightness and color temperature by adjusting a light amount of red, green and blue LEDs. Also, the LED carries advantages suitable for a smaller-sized and lighter-weight LCD panel. Therefore, of late, the LED has been actively employed as a backlight source of the LCD panel.
An LCD backlight adopting the LED is broken down into an edge-type backlight and a direct-type backlight according to location of a light source. In the former, a light source of an elongated bar shape is disposed at an edge of the LCD panel to irradiate light onto the LCD panel using a light guide plate. In the latter, a surface light source with a substantially identical area to the LCD panel is disposed below the LCD panel to directly irradiate light onto the LCD panel.
FIGS. 1 and 2 illustrate arrangement of red (R), green (G) and blue (B) LEDs of a conventional surface light source.
The surface light source 10 for use in a conventional direct-type LCD panel emits white light by combining the red (R), green (G) and blue (B) light together. Thus, as shown in FIG. 1, a plurality of LED units (U) are arranged to define a square shape. In each of the LED units U, the red, green and blue LEDs 11, 12 and 13 are disposed within a proximity to respective vertices of a triangle. Alternatively, as shown in FIG. 2, a plurality of LED units U are arranged to define a triangular shape. However, when the LED units U are arranged to define a square shape as shown in FIG. 1, the red LEDs 11 are located with such density that a red line appears in the display.
Meanwhile, when the LED units U are arranged to define a triangular shape as shown in FIG. 2, the red, green and blue LEDs are relatively evenly disposed. However, a light source including the red, green and blue LEDs 11,12, and 13 in each of the LED units U is arranged such that the LED unit U can produce white light. Thus, to ensure the light source to maintain appropriate brightness level with respect to the other light sources adjacent thereto in the triangular shape, the LED units U should be balanced with one another and the light sources of each of the LED units should be balanced with one another in an overall backlight unit. This accordingly renders it hard to manufacture the backlight unit or degrades quality thereof.
Also, a difference in the light amount of the red, green and blue LEDs may adversely affect uniformity, or degrade contrast uniformity despite good color uniformity.
That is, the LED units are shown partially red or partially blue. Also, with higher temperature, each color is darkened more to hardly ensure a properly functional white surface light source.
Therefore, in the conventional surface light source 10 and the LCD backlight unit having the same, colors are added together with limitation, thereby not realizing uniformly-distributed white light.